Selective adsorbent fabric for water purification

ABSTRACT

A water purification chamber is provided. In one embodiment, a system comprises a purification chamber comprising a selective adsorbent activated carbon fiber fabric including one or more selective functional groups that bind arsenic.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 15/669,557,filed on Aug. 4, 2017, which is a continuation of U.S. patentapplication Ser. No. 14/214,196, filed on Mar. 14, 2014, which in turnclaims the benefit of U.S. Provisional Application No. 61/802,514, filedMar. 16, 2013. Applicant's prior applications are incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present disclosure relates generally to apparatus, systems andmethods related to drinking water purification.

BACKGROUND

The pollution of ground and drinking water by metalloids, especiallyarsenic, a wide range of toxic metals, such as but not limited to, lead,mercury, cadmium, chromium, nickel, iron, cupper, platinum, andpalladium, as well as various organic chemicals, has attractedincreasing attention in recent decades throughout the world.Particularly, the contamination of water by arsenic has been one of themost serious health hazards and its remediation to the Level of Concern(LOC) (10 ppb) has proven challenging.

The presence of arsenic in waterways is due to both natural andanthropogenic causes. For example, arsenic may be released intowaterways due to volcanic activity and from erosion of natural depositssuch as rocks and terrain that has been burned due to forest fire.Further, arsenic may be released into waterways due to agriculturalrunoff, industrial production waste runoff, etc. For example, somefertilizers contain arsenic and further, industrial practices such ascopper smelting, mining, and coal burning also contribute to arsenic inthe environment.

Consuming excessive amounts of arsenic from drinking water maycontribute to a number of mild to severe health effects. For example,arsenic has been linked to thickening and discoloration of the skin,stomach pain, nausea, vomiting, diarrhea, numbness of the extremities,partial paralysis, and blindness. Further, arsenic has been credited asa carcinogen and linked to cancer of the bladder, lungs, skin, kidney,nasal passages, liver, and prostate, as well as a factor contributing tocardiovascular disease.

Since ground water sources and surface water sources are susceptible toarsenic contamination, it is imperative to purify water from thesesources prior to human and animal consumption. The World HealthOrganization (WHO) and US Environmental Protection Agency (EPA) have setthe arsenic standard for drinking water at 0.010 parts per million (10ppb) to protect consumers served by public water systems from theeffects of long-term, chronic exposure to arsenic. While the EPAstandard applies to municipal water treatment facilities, it isdesirable to remove arsenic from other water treatment systems as well.Indeed, in the United States, the National Resources Defense Councilestimates that over 34 million Americans drink from water supplies withaverage arsenic concentrations that pose unacceptable cancer risks.

Arsenic removal technology can be applied to large scale water treatmentsystems, small scale water treatment systems, point-of-use watertreatment systems, well water treatment systems, portable watertreatment systems, and other systems.

Previous solutions for removing arsenic from drinking water involveprocesses/technology such as flocculation, modifiedcoagulation/filtration, modified lime softening iron oxide adsorption,activated alumina, ion-exchange, reverse osmosis, electrodialysis,subterranean arsenic removal (SAR), and metal loaded polymers.Flocculation and iron oxide adsorption techniques generally use aniron-based coagulant to remove arsenic by co-precipitation and/oradsorption. However, the toxic arsenic sludge resulting from coagulationoften clogs the system and the toxic arsenic sludge has to be disposedof by concrete stabilization. While this may be a sufficient short termsolution, the toxic arsenic sludge may leach over time and thus bereintroduced into the environment.

Ion-exchange has traditionally been used as a water-softening processand has some ability to remove arsenic. However, arsenic exists in twooxidation states in water depending on the oxidation-reductionconditions and the pH of the water. As(III) is usually associated withgroundwater under anaerobic conditions, while As(V) is associated withsurface water under aerobic conditions. As(III) is found as the neutralspecies, arsenous acid (H₃AsO₃), below pH 9. As(V) occurs as themonovalent and the divalent arsenate species, H₂AsO₄ ⁻ and HAsO₄ ²⁻,respectively, between pH 6 and 9. Ion-exchange is ineffective inremoving non-charged arsenic(III) species. Further, the presence ofsulfate and high total dissolved solids can significantly affect runlength and maintaining an ion-exchange column is costly and requires askilled technician.

Reverse osmosis and electrodialysis techniques can remove arsenic butresult in high salinity waste water, which presents an issue in that itrequires further waste water treatment. Further, both technologies arehigh cost. SAR technology utilizes an oxidation zone to trap iron andarsenic underground. The technology relies upon soil dwellingmicroorganisms to metabolize iron and arsenic and break these substancesdown to other molecular species. Such a technology is extremelyexpensive to develop and operate. In addition, this technique is notsimple and requires well simulated (calculated) and balanced aquiferoxidation. Otherwise, the oxidation procedure will just lead to arsenicand iron co-precipitation rather than adsorption, resulting in thesubsequent release of arsenic. Metal-loaded polymers and granular metal,especially Fe(III) are interesting due to the possibility to remove bothAs(III) and As(V), however, the arsenic binding is pH dependent andthere remains the possibility of releasing the impregnated metal insolution and adversely affecting the quality of drinking water

SUMMARY

Embodiments for water purification systems are provided. In oneembodiment, a system comprises a purification chamber comprising aselective adsorbent activated carbon fiber fabric including one or moreselective functional groups that bind arsenic. The selective adsorbentfabrics may be differently functionalized and may include anarsenic-selective functional group configured to adsorb one or moreionic structures of arsenic.

One approach to overcome at least some of the issues presented above isto use a selective adsorbent fabric to selectively remove one or morearsenic species from contaminated water. In some embodiments, theselective adsorbent fabric may include an arsenic-selective functionalgroup that binds at least one arsenic ionic species via adsorption. Forexample, the arsenic-selective functional group may sequester As(V)and/or As(III) species from water in which such ionic species arepresent. The selective adsorbent fabric may at least reduce the need fordownstream waste water treatment since the selective adsorbent fabricdoes not produce a toxic arsenic sludge like previous methods. Further,such a selective adsorbent fabric may be easily manufactured and costeffective for use in any water treatment system.

It will be appreciated that the selective adsorbent fabric may be of anysuitable size and geometric shape to accommodate virtually any type ofwaste water treatment system. For example, the selective adsorbentfabric may be configured for a large scale water treatment facility, asmall scale water treatment facility, a point-of-use water treatmentsystem, a well water treatment system, a portable water treatmentsystem, and other systems.

The adsorbent fabrics may selectively adsorb arsenic, while precursorsof the adsorbent fabrics may also adsorb various hazardous organictoxins such as, but not limited to, industrial effluent, pesticides, andvarious sources of Endocrine Disrupting Chemicals (EDCs) which have beengaining increasing concerns over their possible effects on human health.The pollution of ground and drinking water by the above mentionedorganic chemicals has attracted increasing attention in recent decadesall over the world.

The fabrics disclosed herein and treated physico-chemically also adsorba wide range of toxic metals, such as, but not limited to, lead,mercury, cadmium, chromium, nickel, iron, cupper, platinum, andpalladium.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings, in which thelike references indicate similar elements and in which:

FIG. 1A shows a schematic illustration of an example water purificationsystem, specifically a point-of-entry (P-O-E) type water purificationsystem, according to an embodiment of the present disclosure.

FIG. 1B shows another schematic illustration of an example waterpurification system, specifically a pitcher type water purificationsystem, according to an embodiment of the present disclosure.

FIG. 1C shows another schematic illustration of an example waterpurification system, specifically a point of use type (portable) waterpurification system, according to an embodiment of the presentdisclosure.

FIG. 1D shows a schematic illustration of an example water purificationsystem according to an embodiment of the present disclosure.

FIG. 2 shows a schematic illustration of an example purificationcartridge (spiral-wound module) for use in the systems shown in FIGS.1A, 1B, and 1C according to an embodiment of the present disclosure.

FIG. 3 shows a schematic illustration of a bottom plate of an examplepurification cartridge (flat module with zig-zag channel module) for usein the systems shown in FIGS. 1A, 1B, and 1C according to an embodimentof the present disclosure.

FIG. 4 provides a cross-sectional view of an example selective adsorbentfabric (ACF-SBX) included within the purification cartridge or modulewhich adsorbs a wide spectrum of organic toxins with differenthydrophobicity, hydrophilicity (S, strong; W, weak), and molecular sizesas well as arsenic (As(III) and As(V)).

FIG. 5 shows a schematic illustration of an example surface-modifiedselective adsorbent fabric interacting with selected highly hydrophobicorganic toxins and ionic species of the selected toxins, such as As(III)and As(V) that interact with the example surface-modified selectiveadsorbent fabric according to an embodiment of the present disclosure.

FIG. 6 provides an example overview of selected surface modifications offiber to prepare specific adsorbent fabrics interacting with selectedtoxins.

FIG. 7 shows a schematic of the synthesized ACF functionalized witharsenic-specific ligands

FIG. 8 shows methods for thiolation of benzylic halides.

FIGS. 9 and 10 show example measurements of arsenic (As(V)) adsorptionby the functionalized carbon fibers according to embodiments of thepresent disclosure.

FIG. 11 shows effects of competitive ions on the adsorption of AS(III)and As(V) to ACF-SH (III) according to embodiments of the presentdisclosure.

FIG. 12 shows results of a repetitive application of toxic chemicalsolution on the column packed with ACF-SBX.

FIG. 13 is a flow chart illustrating a method for purifying water.

DETAILED DESCRIPTION

Exemplary purification systems for use in water treatment systems areillustrated herein. The purification system may optionally include oneor more reservoirs such as an untreated reservoir and a treatedreservoir. Further, the purification system may include a purificationchamber, including one or more purification cartridges, also referred toherein as filtration modules. Briefly, by directing the untreated waterthrough the filtration module, refreshed or treated water, also referredto herein as purified water, may be generated and used as clean water.Untreated water may include toxins such as arsenic from natural and/oranthropogenic sources, and such toxins may not be desirable in drinkingwater for human and animal consumption, for example.

Briefly, FIGS. 1A, 1B, 1C, and 1D are example water purification systemsaccording to the disclosure. FIG. 1A shows a schematic illustration ofan example water purification system 1, specifically a point-of-entry(P-O-E) type water purification system, according to an embodiment ofthe present disclosure. FIG. 1B shows another schematic illustration ofan example water purification system 10, specifically a pitcher typewater purification system, according to an embodiment of the presentdisclosure. FIG. 1C further shows another schematic illustration of anexample water purification system 20, specifically a point of use type(portable) water purification system, according to an embodiment of thepresent disclosure. FIG. 1D shows another schematic illustrating of anexample water purification system 25. It should be appreciated thatthese illustrations are for example and not intended to limit the typesof configurations that the filtration modules can be applied. As such,these systems are provided for illustrative purposes and not to limitthe disclosure.

As shown in FIG. 1A, each of the water purification systems may includea purification chamber 2 including a filtration module, such as, but notlimited to a spiral wound (A) module or a flat module with zig-zagchannel B. Adsorbents (functionalized activated carbon fibers (ACF))adapted to selectively bind arsenic and/or other toxins may be housed inthe filtration module.

It should be appreciated that although the reservoir (water tank) andpurification chamber are shown as separate devices linked throughcouplers, such as a tubing system 3, one or more the chambers and/orreservoirs may be integrated together. Typically, the purificationchamber is disposed intermediate the untreated reservoir and the treatedreservoir, however other configurations may be possible. For example,FIG. 1D shows a purification system 25 including similar components asFIG. 1A, but also including an untreated water reservoir 5.

It should be appreciated that a tubing system may include fluid inflowand fluid outflow. Further, the tubing system may be a conduitconnecting a fluid source (such as a ground water source) to thepurification chamber. The tubing system may be continuous, and mayconnect various components, such as one or more reservoirs and thepurification chamber. Various pumps, flow meters, pressure gauges, andtoxin detectors may be provided to enable flow into and out of thepurification chamber and reservoir(s).

Fluid, such as untreated water, may flow (or be pumped) into anuntreated reservoir in the direction of the arrow. Untreated water maybe stored in the untreated water reservoir, and when needed, may flowdownstream.

The untreated water temporarily stored in the untreated water reservoirmay flow (or be pumped) into the purification chamber in the directionof the arrow. The purification chamber may remove toxins from theuntreated water using one or more toxin traps. For example, in someembodiments, the purification chamber may include a filtration modulewith fibers as described in more detail below. These fibers may becapable of trapping or retaining arsenic and/or other toxins. Once thetoxins are removed, the water may be considered to be purified such thatit is refreshed water. In some embodiments, the purification chamber mayinclude, in addition to the toxin trap, one or more semi-permeablemembranes to separate small particles which may be contained in thewater such as ground water. In other embodiments, the purificationchamber may be configured without a semi-permeable membrane or the like.

For example, the filtration module may include a selective adsorbentfabric that selectively removes toxins. The selective adsorbent fabricmay adsorb arsenic from the untreated water flowing through purificationchamber in an example. As described in more detail below, the selectiveadsorbent fabric may reduce the concentration of arsenic in theuntreated water such that water exiting purification chamber includesminimal arsenic, and hence, may be referred to as purified water in thisrespect. The fabrics disclosed herein and treated physico-chemically mayalso adsorb a wide range of toxic metals, such as, but not limited to,lead, mercury, cadmium, chromium, nickel, iron, cupper, platinum, andpalladium.

As described in more detail below, the fabric may be disposed within thefiltration module to maximize water flow contact. In some examples, thefiltration module may be a flat module configuration or a spiral wrappedconfiguration. Although these two modules are described in detail below,it should be appreciated that different configurations of the fabricwithin the cartridge are possible and are within the scope of thedisclosure.

Treated water may flow (or be pumped) from the purification chamber to atreated water reservoir or other clean water outlet. It will beappreciated that treated water may flow downstream to an additionalwater treatment process and/or to a municipal end point (e.g. a faucet),for example. In some examples, highly contaminated water may beredirected back through the system until the toxins are sufficientlyremoved.

It will be appreciated that the directionality of the water flow isprovided by way of example and as such is not meant to be limiting. Thetubing system may be configured in any suitable form to transport waterin any suitable direction. For example, one or more sections of tubingsystem may redirect the water flow in another direction than thoseillustrated in FIGS. 1A, 1B, 1C, and 1D. As such the spatialrelationship between the optional one or more reservoirs and thepurification chamber may be linear or non-linear. Further, the systemsmay include additional and/or alternative components than thoseillustrated in the example figures.

In some embodiments, the size requirements may be so reduced as toenable the purification system to be portable. By reducing the size ofthe purification system, a user may purify water in remote environments,for example, backpackers and travelers may use such a portablepurification system. Further, pitchers and other systems may utilize thefiltration module described herein.

It will be appreciated that various sensors may be used to monitor waterquality, as shown in FIG. 1D. The sensors may include, but are notlimited to, a pH sensor, electric conductivity (EC) sensor, and compactspectroscopic sensors. In some embodiments, redundant sensors may beemployed to ensure high water quality in large scale water treatmentsystem. A computer and/or smart phone (not shown) may be used to receiveinformation from the sensors, control the pumps, and record the relevantdata. Although not shown, it should be appreciated that variouselectronics may be provided within the water purification system tofurther control and monitor the purification process. Moreover, a userinterface may be provided such that a user may have immediateinformation regarding the controls, sensors, and system control inputs.

It should be noted that in the disclosed system water is pumped throughthe purification chamber using one or more pumps. In some embodiments,the pumps may be roller pumps, while in alternative embodiments, thepumps may include air pumps, electrical pumps, manual pumps, or anycombination thereof. In some embodiments, the pumps may be capable ofadjusting the flow rate of the respective fluid that the respective pumpis pumping.

In some embodiments, the purification chamber (or filtration module) maybe manually detached from the tubing system, sensors, and other watertreatment components and discarded and replaced with a new purificationchamber. Thus, the filtration module may be considered a replaceablecartridge. As another alternative, the removed purification chamber maybe dismantled to replace one or more disposable components housed withinthe purification chamber, such as an arsenic-selective fabric or asupport screen. Once the disposable purification chamber component isreplaced with a new component, the purification chamber housing may beclosed and the purification chamber may be reattached to its originallocation in the water treatment system.

FIG. 2 shows a schematic illustration of an example purificationcartridge 30, also referred to as a filtration module, for use in thesystem shown in FIGS. 1A-1D according to an embodiment of the presentdisclosure. The example filtration module may be comprised of a housing32 having a fluid flow inlet 34 and at least one fluid flow outlet 36.The inlet and outlet may be part of a tubing system such that thefiltration module is interposed between an untreated fluid reservoir anda refreshed fluid reservoir or clean water outlet, as described above.

As a non-limiting example, an inlet may be disposed in a cartridge top.The cartridge top may be configured to fit or couple to a cartridge orchamber housing. Coupled with or contained in the cartridge top andcartridge housing may be sealing devices, such as one or more O-ringsand/or gaskets, such as a bottom gasket. Such sealing devices may beconfigured to maintain the system as a closed system and prevent leakageof water from the housing.

Further contained within the filtration module may be a selectiveadsorbent fabric 38. This selective adsorbent fabric may remove toxinsfrom the water while substantially maintaining the appropriate levels ofminerals which influence the taste of the water as well as promotedesired body salt balance. The fabric may be formed of a sufficienttortuosity and thickness to ensure good contact with the water flow.Further, the fabric may be wrapped, wound, or otherwise positioned toincrease the surface area of the fabric to the water flow.

As described above, untreated water (toxin-laden water) may beintroduced into the filtration module through an inlet. The untreatedwater may encounter the selective adsorbent fabric. The toxins may becaptured by the fabric and retained such that refreshed water exitsthrough an outlet. In some embodiments, the toxins may be retainedwithin the fabric or along the screen. In other embodiments, a secondoutlet, such as elimination port, may be provided to remove the trappedtoxins. Toxins may be released through the elimination port such thatthe toxins are not retained in either the purification chamber orcirculated back to a reservoir.

FIG. 2 further illustrates an example configuration for the filtrationmodule. Specifically, the filtration module may be a spiral wound designor configuration. The spiral wound design is described in more detailherein.

Turning now to FIG. 3, FIG. 3 provides a schematic illustration ofanother example filtration module 40. In the illustrated example, thefiltration module includes a flat module configuration (with zig-zagchannel module).

Regardless of the configuration, the toxin-laden water is directed intothe filtration module (such as the module in either FIG. 2 or FIG. 3)through the ground/well water inlet or other water inlet and flowsthrough the module along the fabric path to the clean water outlet. Theselective adsorbent fabric may contain one or more fibers, such asactivated carbon fibers (ACF), ACF-SH which catches both As(III) andAs(V), and ACF-SBX which catches As(V) and a wide spectrum of toxicorganic chemicals. The ion-selective fibers may be configured toselectively capture one or more toxins. Although described in relationto a single fiber, it should be appreciated that the fabric/fiber mayinclude one or more fibers and such fabric/fibers may interact togetherto form a toxin trap.

It should be appreciated that any suitable fiber may be used. In someembodiments, the fabric may be composed of carbon fibers or othersuitable fiber-like materials, including plastics, polymers, resins,silicone, cotton, etc. Further, in some embodiments, as an alternative,particles, aggregates, weaves, rings, tubes, such as grapheme, carbonnanotubes, etc., may be used in place of fibers. In some embodiments,the fibers may be acid-treated or oxidized, while in other embodiments,the fibers may not be acid-treated or oxidized.

Additionally, the fibers may be activated fibers or non-activatedfibers. Further, the fibers may be nanofibers. For example, in oneembodiment, the fibers may be activated carbon fibers. Activated carbonfibers may be made by the carbonization and activation of precursorfibers (e.g. polyacrylonitrile, phenol resin, pitch, rayon, cotton,etc.) at high temperature and in the flow of air containing oxygen, orin the flow of inert gas such as nitrogen or argon.

For example, activated carbon may be made by burning hardwood,nutshells, coconut husks, cottons, animal bones, pitch,carbon-containing polymers (such as rayon, polyacrylonitrile, etc.), andother carbonaceous materials. The charcoal becomes “activated” byheating it with steam, carbon dioxide, or carbon monoxide to hightemperatures in the absence of oxygen. This heating removes any residualnon-carbon elements and produces a porous internal microstructure withan extremely high surface area.

Further, activated carbon fibers may be subject to washing treatmentsand/or further heat treatment to increase consistency of batch-to-batchsamples. As one example, activated carbon fibers may be heated at 325°C. for 8 hours. As another example, activated carbon fibers may beheated at 300° C. for 24 hours. These additional heat treatments mayincrease the surface area, pore size stability, meso pores, crystallinestructures, C—O and C═O (if under the air), and decrease in hydrogencontent. Therefore, it will be appreciated that activated carbon fibersmay be subject to any pre-treatment including washing and heating, andfurther, that duration, frequency, temperature, etc., of washing/orheating may be a suitable value.

In one embodiment of the present disclosure, the selective adsorbentfabric may include one or more arsenic-selective functional groups, oranother arsenic- or toxin-selective functional group. Alternativeembodiments may include traps selective for other waste products to bepurified including, but not limited to, mercury, lead, cadmium, copper,and other heavy metals, ammonia, and other organic and inorganiccontaminants.

Any suitable fabric may be used as a selective adsorbent fabric. Thearsenic-selective fibers may be disposed in any orientation, forexample, the fibers may be in an overlapping, bi-parallel orientation.It should be appreciated that the fibers may be oriented in a variety ofpatterns, including a chaotic arrangement. Fibers may be uniform orvariable sizes within fabric. Although not illustrated in FIG. 2, boundenzymes and/or microbial biofilms may be disposed along the fibers foruse in decomposition of arsenic. For example, arsenic may be metabolizedby enzymes and/or microbial species via methylation, demethylation,oxidation, and/or reduction reactions. Other select enzymes, fordecomposition and/or trapping of other toxins, may also be selectivelydisposed along the fibers.

Fibers may be produced using a furnace in house and/or be commerciallyavailable activated fibers (AF). In some embodiments, activated carbonfibers (ACF) and fabrics are used. One exemplary fiber for use in thepurification system described herein may be a basket weaved fiber with aspecific surface area of 600/m²/g to 2,000 m²/g. Another exemplary fiberfor use in the purification system described herein may be felt type,which may have a similar specific surface area. Although an exemplaryfiber is provided, other fabrics and fibers may be used with wide rangesof density, specific surface area, pore structures, and pore sizedistributions without departing from the scope of the disclosure. Forexample, other commercially-available economical fibers or preparedfibers/fabric may be used because the economy of the water purificationsystem is one of the most critical factors.

It should be noted that the fibers may have a three-dimensionalconfiguration. Within the three dimensional configuration, the fibersmay be disposed such as to form macropores, mesopores, micropores, andnanopores, or structures that may contain select functional groups. Suchstructures may be configured to trap or retain select ions and organictoxins. For example, the pores may be charged to selectively trapoppositely-charged ions. In one example, the pores may be positivelycharged, thus configured to attract and trap negatively-charged ions,such as arsenic(V) and chemicals rich with functional groups withpartially negatively charged and/or high electron density and/or rich inπ electrons.

Once a fabric is selected, the fabric fibers may be prepared for use asthe selective adsorbent fabric. In some embodiments, the fiber surfacemay be modified to increase the concentration of oxygen-containingfunctional groups. The modification to the surface may be such that thesurface of the fiber is oxidized. For example, the surface may bemodified by treating the selective adsorbent fabric with nitric acid(HNO₃) and sulfuric acid (H₂SO₄) to achieve the addition of carboxylicacid groups and hydroxyl groups to the selective adsorbent fabric. Insome examples, fibers will be functionalized to create functionalizedactivated carbon fibers, such as ACF-SO₃H, ACF-PO₃H and ACF-NH₂; ACFfunctionalized with amino groups (several surface modification methodsare available); ACF-SBX; ACF functionalized with strongly-basicanion-exchange groups as shown in the figures, etc.

Further, the fabric fibers may be additionally prepared for use as theselective adsorbent fabric. In some embodiments, the fiber surface maybe modified to increase the concentration of sulfur-containingfunctional groups, and/or other non-metal-containing functional groups.The modification to the surface may be such that the surface of thefiber is sulfided. For example, the modification to the surface may besuch that the surface of the fiber contains a methyl sulfide (SH), alsoreferred to as a thiol or a mercaptan. For example, the surface may bemodified by treating an oxidized selective adsorbent fabric withthiourea (CH₄N₂S), hydrogen bromide (HBr), and/or sodium hydroxide(NaOH) to achieve the addition of a methyl sulfide to the selectiveadsorbent fabric.

Any suitable method may be used to modify the surface, including, butnot limited to, heat treatments, peroxide treatments, acid treatments,etc. Modification of the surface of the fiber to include high oxygenconcentration and higher relative concentration of carboxylic andhydroxyl groups may provide the functional groups for sulfur binding andenable further modification of the fiber. It should be appreciated thatsurface, as used herein, may be any portion of the fiber that may beexposed or exposable to the water flow.

Additional examples of the filtration modules and the configuration ofthe fabric and water flow path are further illustrated in FIG. 3.Specifically, FIG. 3 provides an example illustration of a bottom platefor water purification as disclosed herein. It should be appreciatedthat the dimensions are provided by way of example and are not alimitation. Any suitable size fabric, system or configuration may beprepared based on the use application for the filtration module.

Returning to FIG. 2, the selective adsorbent fabric 38 (illustratedherein as an ACF-1 fabric) is wrapped around a central core withsufficient tortuosity and thickness to ensure good contact between theradial-flowing feed (e.g., untreated water) and the adsorbent. Anadditional type of activated carbon fiber, illustrated as ACF-2, may beincluded when desired. It should be appreciated that an alternativemethod for constructing the spiral wrapped modules is to wrap pre-wovenACF cloth or fabric around a central core. Further, these ACF clots maybe co-wrapped with an adequate carrier such as polypropylene mesh, sothat the feed solution is forced to travel in a spiral pattern from thecentral feed core to the outer collection shell.

FIG. 4 provides a cross-sectional view of an example selective adsorbentfabric 50 (ACF-SBX) which adsorbs a wide spectrum of organic toxins withdifferent hydrophobicity, hydrophilicity, and molecular sizes as well asAs(V).

FIG. 5 shows a schematic illustration of an example surface-modifiedselective adsorbent fabric 60 interacting with a selected toxin andexample ionic species of the selected toxin that interact with theexample surface-modified selective adsorbent fabric 60 according to anembodiment of the present disclosure. FIG. 5 provides specific ligandsthat can be attached to activated carbon fibers (ACF) by physical andchemical treatments. In an example, the groups X, Y, and Z of FIG. 5refer to X; —SH, Y; —COOH, Z; —OH, —C═O, —NH, and etc. It should benoted that some functional groups are introduced from opposite screen in3-dimensional scheme. Diversity of coordination schemes of arsenic withfunctional groups in proximity in ACF-SH (III) matrix could be possible.Namely, both As(III) and As(V) are able to coordinate with multipleneighboring functional groups, resulting in stabilized arsenic absorbed.Some hydrogen bonds will be formed via surface coordinated watermolecule. Secondary interaction of arsenic with π electrons of carbonaromatic rings are not shown.

FIG. 6 provides an example overview of selected surface modifications offibers to prepare specific adsorbent fabrics interacting with selectedtoxins. As used herein ACF refers to Activated carbon fiber; ACF-Hrefers to heat treated ACF (Stabilized nano-/micro-pore structures,Increased surface area, Increased crystal structures, Decreased hydrogencontent, Increased C—O and C═O); ACF-OH refers to acid oxidized ACF atroom temperature (Increased C—O, C═O and —COOH); ACF-SO3H and ACF-PO3Hrefer to ACF functionalized with —SO3H and —PO3H, respectively. ACF-NH2refers to ACF functionalized with an amino group (several surfacemodification methods are available); and ACF-SBX refers to ACFfunctionalized with strongly-basic anion-exchange groups such astrialkylamines (methylamine, ethylamines and other alkylamines). Thereare several preparation methods available for ACF-SBX.

ACF-SBX, ACF-H, ACF-OH and ACF-NH2 are all reasonably good adsorbentsfor various organic toxins. Particularly, ACF-SBX and ACF-H are verygood adsorbents for various organic toxins, as shown in Table 1 below.

TABLE 1 Kinetic Data for Adsorption of Organic Toxins to ACFs. Conc.ACF-H ACF-OH ACF-SBX Chemical M.W. (mg/dL) 50% >95% 50% >95% 50% >95%Log P^(‡) HBD^(▪) HBA^(▪) anthracene 178.2 0.9 ^(♦)0.5  53.0 0.4 30.00.4 12.5 4.49 0 0 atrazine 215.7 1.8 2.0 20.0 6.0 (90%) 1.6 10.0 2.61 25 bisphenol A 228.3 10.0 5.0 30.0 45.0 (70%) 4.0 30.0 3.32 2 2 DEHP^(†)390.6 6.9 20.0  80.0 43.3 (92%) 3.8 20.0 7.80 0 4 chloramine-T 227.615.0 3.3 25.0 50.0 (82%) 3.3 25.0 N/A 0 3 chlorobenzene 112.6 16.0 0.3 2.0 0.3  2.0 0.3  2.0 2.84 0 0 p-cresol 108.1 15.0 2.0 30.0 20.0 (89%)1.5 60.0 1.97 1 1 deca-BDE^(†) 959.2 0.3 0.4 n.d. n.d n.d. 0.5 n.d. 9.970 1 2,4-dichlorophenol 163.0 15.0 1.5 30.0 2.6 (92%) 2.3 30.0 3.17 1 12,4-D^(†) 221.0 15.0 5.0 60.0 15.0 (85%) 5.0 30.0 2.81 1 3o-dichlorobenzene 147.0 14.0 1.5  3.0 1.5 3.0 0.8  3.0 3.38 0 0p-dichlorobenzene 147.0 17.0 1.0  2.0 1.0 2.0 1.0  2.0 3.44 0 0 diethylphthalate 222.2 15.0 5.0 50.0 60.0 (69%) 3.5 25.0 2.42 0 4 diuron 233.15.0 3.0 15.0 30.0 55.0 3.0 15.0 2.77 1 1 ethylbenzene 106.2 15.0 0.3n.d. 0.3  0.5 0.3 n.d. 3.15 0 0 17β-estradiol 272.4 4.6 0.5 10.0 0.550.0 0.5 10.0 4.03 2 2 4-nitrophenol 139.1 11.0 0.8 20.0 5.0 60.0 1.520.0 1.91 1 3 NDEA 102.1 15.0 3.8 (93%) 30.0 (59%) 4.6 60.0 0.48 0 34-nonylphenol 220.4 15.0 2.0 30.0 57.0 (73%) 5.0 45.0 5.76 1 1 triclosan289.5 5.0 2.5 55.0 26.0 (91%) 1.7 46.7 4.53 1 2 uric acid 168.1 15.0 3.030.0 15.0 60.0 3.0 30.0 −2.92  4 3 ^(♦)Estimated time to achievedesignated toxin removal (min). All experiments were performed inStandard Synthetic Test Water (STW) which was prepared by dissolving31.90 mg Na₂SiO₃•5H₂O, 252.06 mg NaHCO₃, 61.60 mg MgSO₄•7H₂O, 50.85 mgMgCl₂•6H₂O, and 147.20 mg CaCl₂•2H₂O in 1 L ultra-pure DI water. The pHis adjusted to 6.9~7.0. ^(†)DEHP; bis(2-ethylhexyl)phthalate, deca-BDE;decabromodiphenyl ether, 2,4-D; 2,4-dichlorophenoxy acetic acid.^(‡)Logarithm of measured partition coefficient, ^(▪)HBD; hydrogen bonddonors, HBA; hydrogen bond acceptors.

ACF-SBX was the best sorbent for rapidly removing a wide spectrum oforganic chemicals. ACF-H was found to be a fairly good adsorbent as wellalthough it was not a good adsorbent for anthracene, DEHP, and someother tested chemicals. ACF-SBX also appears to be a good sorbent forchemicals rich in hydrogen bond acceptors. Although the levels of all ofthese toxic chemicals in ground water are generally quite low (ppblevel), initial adsorption studies were performed at much higherconcentrations (ppm level) to readily screen them with minimal errors.One liter of water contaminated with total 100 ppb range (highcontamination level) of typical organic toxin mixtures will be rapidly(seconds level) removed by 0.1 g ACF-SBX. The loading capacity ofACF-SBX and ACF-H for most of toxins in Table I is the range of 150mg-300 mg/g. Assuming a total organic contamination of 500 ppb (one ofthe highest cases in the drinking water/well water), 14 liters ofdrinking water per day (standard for four member family), the cartridgecontaining 100 gram of ACF-SBX filter would clear organic toxins throughone year. Thus, ACF-SBX will be very powerful water purifier andsuitable for use as water faucet attached purification device. Thestrength of ACF-SBX is that it is able to adsorb As(V) in addition tovarious toxic organic chemicals.

It should be appreciated that there is diversity of coordination schemesof arsenic with functional groups in proximity in a ACF-SH (III) matrixas shown in FIG. 5. As(III) is capable of forming three strong covalentbonds but often interacts weakly with additional electron donor ligands.Usually, one weak donor-acceptor interaction predominates. However, whenelectron donors are appropriately arranged, the total inner coordinationnumber of As(III) can include as many as three weak donor-acceptorinteractions in addition to three strong covalent bonds. Otherion-species, As(V) can form as many as five strong covalent bonds.Pentavalent arsenic can also behave as a Lewis acid and weakly interactwith additional electron donor ligands. Some hydrogen bonds will beformed via surface coordinated water molecule as shown in FIG. 5.Secondary interaction of arsenic with π electrons of carbon aromaticrings is not shown.

The strength of the ACF material is the ability to vary pore dimensionsand customize pockets with multiple ligands to attract and sequesterarsenic. N and O heteroatoms can be positioned within and upon the ACFmaterial to take advantage of favorable non-bonding donor-acceptorinteractions with arsenic. The ACF material can be functionalized withligands to attract and tightly sequester arsenic through multiplebonding interactions. The proximal location of different functionalgroups with complimentary bonding modes can enhance binding of arsenic.Optimum binding of arsenic is dependent on the location and proximity ofligands as well as the dimensions of the layers and pockets within theACF material.

The degree of the proximity (distance) and number of coordinationbetween arsenic and functional groups will be controlled by thepreparation methods of ACF-SH (III) from the ACF-H including theoxidation of ACF-H as well as the heat treatment condition of ACF toprepare the ACF-H. And, the apparent maximal adsorption capacity ofACF-SH (III) varies, for example in a range of 5 mg/g to 30 mg/g, forboth As(III) and As(V) in the STW environment. ACF-SH (III) is also aneffective adsorbent for lead and mercury in the STW environment withadsorption capacity of more than 60 mg/g for both toxic metals.

FIGS. 7 and 8 illustrate example modifications to the ACF to attacharsenic-specific ligands to the fibers. FIG. 7 shows a schematic of thesynthesized ACF functionalized with arsenic-specific ligands. FIG. 8shows methods for thiolation of benzylic halides.

The following case studies are provided as examples of the functionalityof various arsenic-selective functional groups incorporated intoactivated carbon fibers.

Case Study #1: Preparation of Chloromethyl ACF (ACF-CH₂Cl)

ACF-CH₂Cl is a key intermediate in the production of a subset of thearsenic-selective fabric fibers and also for ACF-SBX production,presented below. ACF-CH₂Cl was prepared through two different routes.The first method used the reaction of the ACF with paraformaldehyde andacetamide in the presence of sulfuric acid under a nitrogen atmosphere.This method has been readily utilized for the chloromethylation ofaromatic compounds. Briefly, the ACF were heated in the sulfuric acidcontaining paraformaldehyde (1 equivalent) at 55° C. for 5 hours.Acetamide (3 eq.) was added to the reaction medium in portions andmaintained the reaction mixture at 55° C. for 8 hours. ACF wasextensively washed with water, toluene and finally ether before dryingin vacuo. The ACF was placed in xylene containing phosphorus oxychloride(2 eq.) and dimethylformamide (1 eq.), and subsequently the mixture washeated to reflux for eight hours under a nitrogen atmosphere. TheACF-CH₂Cl was washed with water and ether to remove any unreactedmaterials and contaminants. The ACF-CH₂Cl was then dried in vacuo, andstored under nitrogen until use.

In the alternative method, ACF was reacted with chloromethylmethyl ether(1. equivalent) and zinc chloride (0.1 eq) in dichloromethane at 50° C.for 8 hours under a nitrogen atmosphere. The ACF was extensively washedwith methanol, and subsequently with water before drying in vacuo.ACF-CH₂Cl was stored under nitrogen until use. The ACF-CH₂Cl may be usedto prepare ACF-SH (II), ACF-NH—SH (I), ACF-NH—SH (II), and ACF-SNX,presented below.

Case Study #2: ACF-SH (II)

ACF-SH (II) was prepared by reaction of ACF-CH₂Cl with sodiumhydrosulfide. Methods for the preparation of aromatic and aliphaticthiols have been extensively reported in the literature. Briefly, theACF-CH₂Cl was placed in water containing sodium sulfide (1 eq.) and themixture heated to reflux for 8 hours under a nitrogen atmosphere. Thereaction was terminated by soaking the ACF in hydrochloric acid. TheACF-SH was washed extensively with water and dried in vacuo. Theprepared ACF-SH (II) was stored under nitrogen until use.

Case Study #3: ACF-NH—SH (I)

The ACF-NH—SH (I) was prepared through the reaction of the ACF-CH₂Clwith 2-aminoethanethiol (1 eq.) in water at 60° C. for 8 hours. Thereaction was carried out under a nitrogen atmosphere. The ACF-NH—SH (I)then was extensively washed with water before drying in vacuo. Theprepared ACF-NH—SH (I) was stored under nitrogen until use.

Case Study #4: ACF-NH—SH (II)

The ACF with multiple thiol groups (ACF-NH—SH (II) was prepared byreacting ACF-CH₂Cl with 3-amino-1,2-propandiol (1 eq.) in water at 60°C. for 7 hours under a nitrogen atmosphere. The ACF was washed withwater, and subsequently refluxed with thiourea (1 eq.) and hydrobromicacid (1 eq.) in water for 16 hours under a nitrogen atmosphere. Thereaction was cooled to medium to room temperature and sodium hydroxidewas added (2 eq.), and then the reaction was refluxed medium again for16 hours under a nitrogen atmosphere. The functionalized ACF wasextensively washed with water until the solution reached to a neutralpH. The ACF-NH—SH (II) was dried in vacuo and stored under nitrogenuntil use.

Case Study #5: ACF-SBX

The ACF-SBX which is ACF functionalized with strongly-basicanion-exchange groups was prepared by reacting ACF-CH₂Cl withtrialkylamines. This method is commonly used to functionalizepolystryrene resins with strongly basic anion exchange groups. Theresulting ACF-SBX was washed with ether and water, and then washed thesalt form with water until the pH reached neutral. ACF-SBX was stored inwater until use. Briefly, the ACF-SBX was prepared by reacting theACF-CH₂Cl with trimethylamine (1 eq.) in water at 55° C. for 5 hoursunder a nitrogen atmosphere. The ACF was washed with water, dilutesodium hydroxide and water. The ACF-SBX was converted to the chlorideform by treating it with 0.1 M hydrochloric acid. The fabric was washedextensively in water before drying in vacuo.

The Case Study #7: ACF-SH

ACF-SH may be prepared without utilizing the ACF-CH₂—Cl. The ACF-SH wasfirst prepared via synthesis of the intermediate, chloromethyl ACF(ACF-CH₂Cl) and was designated ACF-SH (II). We also attempted to prepareACF-SH, designated as ACF-SH (I), through a more direct reaction of ACFwith thiourea. This was to pursue the more economic route of thepreparation of ACF-SH. Specifically. ACF was reacted with thiourea (1eq.) and hydrobromic acid (1 e.q) in water at 100° C. for 16 hours undera nitrogen atmosphere. The reaction was cooled to medium to roomtemperature and added sodium hydroxide (2 eq.) and then the medium wasrefluxed for 16 hours at 100° C. under a nitrogen atmosphere. Themodified ACF was extensively washed with water until the solutionreached to a neutral pH before drying in vacuo. The prepared ACF-SH (I)was stored under nitrogen until use.

Case Study #8: ACF-SH (III)

We proposed that the increase in —OH groups of ACF would increase thesubsequent formation of —SH groups on the ACF with thiourea, describedpreviously. Therefore, we attempted to increase the density of —OHthrough rigorous oxidation of ACF according to the method developed inhouse as described below. ACF-SH (III) may be prepared without utilizingthe ACF-CH₂—Cl intermediate. First the acid treated ACF (ACF-OH) wasprepared by reacting ACF with a 50/50 (v/v) mixture of nitric andsulfuric acids. The acid treated ACF was extensively washed with wateruntil the solution reached to a neutral pH before drying in vacuo. Theacid treated ACF was stored under nitrogen until use. Next, the ACF-SHwas prepared using acid treated ACF which is rich in —OH groups.Specifically, the acid treated ACF was reacted with thiourea (1 eq.) andhydrobromic acid (1 eq.) in water at 100° C. for 16 hours under anitrogen atmosphere. The reaction was cooled to medium to roomtemperature and sodium hydroxide (2 eq.) was added and then the mediumrefluxed for 16 hours at 100° C. under a nitrogen atmosphere. Themodified ACF was extensively washed with water until the solutionreached to a pH above 6.0 before drying in vacuo. The prepared ACF-SH(III) was stored under nitrogen until use.

Case Study #9: Measurement of Arsenic Adsorption by the FunctionalizedCarbon Fibers

Adsorption tests were used to measure the interaction of thefunctionalized carbon fibers. At first, we performed the study witharsenate (As(V)) in the absence of competing ions to evaluate theadsorption kinetics and reproducibility of the preparation of fibers.Next, we perform the kinetic studies under the various pH to see whetherfunctionalized ACF can catch arsenate under the changing pH. Next, theinteraction of the functionalized ACFs with As(V) was measured in thepresence of synthetic ground water to see the competitive effects ofcommon anions and cations on the arsenic adsorption of selectedfunctionalized ACF. As there was a large number of samples to beanalyzed in the adsorption experiments and general analysis of fiberssuch as titration, elemental analysis, surface analysis, limited amountsof fiber and a simple shaking method were used instead of a flow throughmethod, although it is known that adsorption/absorption capacities aremuch higher when the arsenic solution is flowed through a column ormodule packed with the ACF.

The adsorption of arsenic. As(V) by functionalized ACF was measured asfollows. One hundred mg of each functionalized ACF (dry wt.) was placedin 20 mL of a test solution in an EDTA washed container at pH 7.0(unless otherwise noted). The samples were shaken for a designated timeperiod and the aliquots were removed for the determination of remainingarsenic. The adsorption (loading) was expressed as the mg of arsenicadsorbed divided by the mass of fabric used. The determined totalarsenic concentration in all test solutions was made mainly by graphitefurnace atomic absorption spectrometry (GFAA; EPA Method 200.9) in houseand occasionally inductively coupled plasma mass spectroscopy (ICP-MS;EPA Method 200.8) for determination of As below 10 ppb.

Although there were some preliminary results in the adsorption kineticstudies using ACF-SH (II) with fixed concentration of arsenics, it wasdecided to use the same fabric amount (100 mg), with varyingconcentrations of arsenic (200 ppb instead of 1 ppm) for all theadsorption tests except isothermal binding experiments. Therefore, firstthe adsorption (binding) kinetic study using ACF-SH (II) to assess theapproximate equilibrium time points of the adsorption, as shown in FIG.11. The reaction medium containing 100 mg ACF-SH (II) and 200 ppbarsenic in 20 mL deionized water (adjusted to pH 7.0) was shaken at 180rpm at 22° C. using an orbital shaker. After each time point, an aliquotwas collected to measure the remaining arsenic by GFAA to determine theadsorbed amount of arsenic. Initial and final concentrations of themetalloids in the test solutions were measured by the analytical methodsdescribed above. Data were used to calculate the bed amount of As(V) tothe functionalized ACF.

As shown in FIG. 9, the arsenic adsorption by ACF-SH (II) apparentlyreaches the first phase of equilibrium after 40-60 minutes of incubation(most likely due to the binding of arsenics to the high affinity bindingsites or external binding sites of ACF-SH (II)). After 40-60 minutes ofincubation, the adsorption (absorption/binding) process still continuedat a much slower rate for almost several hours. This is likely due tothe arsenic binding to the internal binding sites inside the ACF matrix.In this case study, we focused on the first phase of thebinding/adsorption process since we are focusing on the recovery ofarsenic at point of entry (POE) and/or point of use (POU) devices, whichrequire efficient removal of arsenic in a short contact time. Therefore,a shorter (60 minutes) incubation time was employed to evaluate theefficacies of each functionalized ACF.

The first extensive screening of the functionalized ACF was performedusing various pH with a fixed relatively low concentration of arsenic(200 ppb) and a fixed amount (100 mg) of ACF in 20 mL of deionized water(DI water). Each reaction medium was shaken at 180 rpm using an orbitalshaker. After one hour, an aliquot was collected to measure theremaining arsenic by GFAA to determine the adsorbed amount of arsenic.Initial and final concentrations of the metalloids in the test solutionswere measured by the analytical methods described above. Data were usedto calculate the adsorbed amount of As(V) to the functionalized ACF.

In the results all the functionalized ACF preparations showed muchhigher absorption (loading) capacity than that of native ACF forarsenic. In addition. ACF-NH—SH (I), ACF-SH (III) and ACF-NH—SH (II)indicated higher adsorption (loading) capacity of arsenic than that ofACF-SH (II) and ACF-OH. ACF-SBX had relatively high adsorption capacityat pH 6.0. However, the adsorption capacity of ACF-SBX decreased rapidlyin the pH higher than 7.0. Although ACF-SH (II) did not show higheradsorption capacity compared with ACF-NH—SH (I). ACF-SH (III) andACF-NH—SH (III), the reproducibility of the preparation of ACF-SH (II)was one of the best among tested functionalized ACF. Therefore, weincluded this for the remainder of the study. On the other hand, thereproducibility of the preparation of ACF-SH (I) was the lowest amongall the preparations. The preparation also did not have significantadsorption capacity of arsenic. It, along with ACF-Ph-SH and ACF-OH,ACF-SH (I) were excluded from further studies of arsenic adsorptionproperties.

Next, review of the pH dependence of arsenic adsorption to selectedfunctionalized ACF (ACF-NH—SH (I), ACF-SH (III). ACF-NH—SH (III), andACF-SH (II)) was studied in detail between pH 2.0 and pH 10.0. FIG. 10shows the results.

Although ACF-NH—SH (I) showed reasonable adsorption capacity forarsenic, it was not easily reproduced, and was difficult to obtainconsistent arsenic adsorption profiles. ACF-SH (III) and ACF-NH—SH (II)were both promising as excellent arsenic adsorbents under the wide rangeof pH. Therefore, through pH dependence studies of arsenic adsorption tofunctionalized ACF, we determined that the best functionalized ACFs forfurther studies were ACF-SH (III) and ACF-NH—SH (II). However. ACF-SH(II) was used in many of the studies as it is easily and economicallyprepared while still showing reasonable arsenic adsorption capability.In addition, the improvement of the synthetic route of ACF-SH (II) toincrease the adsorption capacity could be feasible.

The elemental analyses of selected functionalized ACFs were performed todetermine elemental composition at normal resolution for each sample,illustrated in Table 2 below. The fabric samples showed that differentdegrees of sulfur, oxygen, and nitrogen atom contents that areconsistent with methods of the treatments of ACF. The method employed inthe preparation of ACF-SH (III) was the most efficient method forincreasing the total sulfur content in the fabric.

TABLE 2 Elemental Composition of Fabric Samples Atomic Percent Sample CH N S O ACF 82.9 1.6 2.4 nd 9.3 ACF-SH (I) 73.1 1.7 2.8 7.2 11.0 ACF-SH(II) 69.1 2.1 3.0 1.6 19.6 ACF-NH-SH (I) 71.6 2.4 3.7 2.6 10.0 ACF-OH55.9 2.3 2.8 0.6 16.6 ACF-SH (III) 51.8 1.6 4.9 18.1 6.8

The next isothermal binding studies were performed using the followingthree functionalized ACF: ACF-SH (III), ACF-NH—SH (II), and ACF-SH (II).The isothermal binding (adsorption) curve was complicated for ACF-NH—SH(II), having multiple adsorption phases and a lack of consistency (datanot shown). The adsorption of arsenic to both ACF-SH (III) and ACF-SH(II) showed good isothermal curves. In review, the arsenic binding toACF-SH (III) was far higher than arsenic binding to ACF-SH (II).Therefore, we focused on ACF-SH (III) to characterize its arsenicremoval capacity.

Next, the adsorption experiments was performed using a standardsynthetic test water (STW) solution (Table 3), containing most of thecommon ions found in drinking/groundwater. Briefly, the functionalizedACF (ACF-SH (III)) was placed in test bottles containing either STWsolution or DI water which were subject to shaking (200 rpm) in atemperature-controlled water bath. After one hour, an aliquot wascollected to measure the remaining arsenic by GFAA. It is encouragingthat ACF-SH (III) maintained at least 70% (at >1 ppm arsenic) and 85%(at below 0.5 ppm) of its arsenic binding (adsorption) capacity in SWT.

TABLE 3 Composition of the Standard Synthetic Test Water (STW) SolutionCations meq/L mg/L Anions meq/L mg/L Na⁺ 3.3 75.9 HCO₃ ⁻ 3.0 183.0 Ca²⁺2.0 40.2 SO₄ ²⁻ 0.5 24.0 Mg²⁺ 1.0 12.2 Cl⁻ 2.5 88.8 SiO2 0.3 20.0 Total6.3 128.3 Total 6.3 315.8

Case Study #11: Evaluation of Functionalized ACF for Removal of BoundArsenic Selected Fibers were Evaluated, Especially, ACF-SH (II) andACF-NH—SH (II), and to Some Extent, ACF-SH (II) for the Development ofModules Composed of Arsenic-Selective Ligand-Anchored ACF.

The first criterion for the evaluation is the optimal combination ofadsorption capacity and regeneration efficiency. Those functionalizedACF, especially ACF-SH (III), show distinct notability in terms ofadsorption capacity of arsenic over a wide range of pH and easilyreproduced preparation through simple synthetic routes. The ACF-SH (III)was superior to any other functionalized ACF tested here in arsenicadsorption capacity in the presence of Standard Test Water (STW). Interms of regeneration, it was found that adsorbed (absorbed) arsenicbound to the ACF-SH (III) matrix and was not easily dissociated.Regeneration of other functionalized ACF including ACF-SH (I) wasaccomplished by changing the ionic concentration or the pH of thesystem.

Options to regenerate ACF-SH (III) by means of changing the ionicstrength of the system and exposure to the arsenic-ACF-SH (III) complexto the low and high pH using 1-10 bed volumes of regeneration solutionare considered. Neither trial proved an effective method of dissociatingbound arsenics from ACF-SH (III). The above mentioned phenomenon isreasonable because ACF-SH (III) shows high arsenic adsorption capacityin wide range of pH and in the presence of salt solution.

The extremely tight binding of arsenic to ACF-SH (III) is not negativeto the intended use. However, consideration is made to methods ofdisposing the recovered arsenic as a stabilized complex with ACF-SH(III). This ACF is light weight and easily forms complexes withstabilizing compounds to mask the ACF-SH (III) matrix.

A major factor in regulating the total cost of any remediationtechnology is the reusability of the adsorbent through regeneration, andthe cost of regeneration of the adsorbent. In some cases, the cost ofregeneration far outweighs the cost of replacement and produces the vastamount of solvent contaminated with arsenic. Therefore, if a simple andcost effective regeneration technique is not readily available, disposalof recovered arsenic as a stable complex is another option in drinkingwater remediation.

The reproducibility in preparing the fibers was the second importantevaluation criteria for this functionalized ACF-based arsenic removaltechnology. In some systems, it was found ACF-SH (III) was superior toall the other functionalized ACF tested in terms of high bindingcapacity in the wide range of pH and in the STW, reproducibility in thepreparation and adsorption assays. As such, in one example, ACF-SH (III)may remove greater than 95% Arsenic (V) from test solutions containing0.05-1.0 mg/L Arsenic (V), and a maximal loading capacity (estimated byisothermal studies) of 5-30 mg of Arsenic (V) per gram of functionalizedACF when incorporated into the tightly packed module. However, theoperational capacity which does not release or remain more than 10 ppbarsenic will be much less and estimated to be around 100 μg/g. Theoperational loading capacities of ACF-PO4, ACF-SO4. ACF-OH and ACF-SHfor removing lead, mercury, cupper (II), iron (II), platinum, nickel andpalladium are generally much higher to be around 20-80 mg/g fiber.

Next, competitive adsorption studies were performed using both As(V) andAs(III). The adsorption of As(III) in the absence of STW is very similarto that of As(V). ACF-SH (III) maintained at least 85-92% of its binding(adsorption) capacity for As(III) in SWT, which is somewhat better thanthat of As(V) (70-85%). As(III) bound very tightly to ACF-SH (III) overa wide range of pH (2-10), which is similar to the case of As(V) bindingto ACF-SH (III) (data not shown). It has been determined that 2 hourstreatment times with 100 ppb for both arsenic species will providecomparable binding data (data not shown). There were no significanteffects of tested well known competitive ions (Fe(II), Fe(III), Cu(II),Mn(II), Mn(IV), nitrate and phosphate) at five times mass equivalent ofAs(V) and As(III) on the adsorption of both arsenic species to ACF-SH(III), under the experimental conditions employed here. Also, >20 ppmoxygen had no effect on either As(V) or As(III) adsorption onto ACF-SH(III). As expected from the previous studies, STW inhibited the bindingof both As(V) and As(III) to ACF-SH (III) at 8% and 13%, respectively.The adsorption capacity of ACF-SH (III) for As(III) and As(V) in thepresence of increasing concentrations of Fe(III) (up to a 50-foldequivalent of As(V) and As(III)) were studied. At 50-fold massequivalents, Fe(III) did not have any significant effect on the removalof As(V) or As(III) by ACF-SH (III), Data not shown

Referring back to FIG. 5, the surface-modified fiber may be capable ofbinding arsenic. FIG. 5 schematically shows arsenic binding to asurface-modified fiber, specifically to a sulfur-treated activated fiber60. As shown, the sulfur-treated activated fiber 60 may includemacropores, micropores, and/or nanopores. An enlargement of such a poreis indicated generally at 62. Pore 62 may include selective functionalgroups ‘X,’ ‘Y,’ and ‘Z.’ For example, a selective functional group X(such as an-arsenic selective group) may be a sulfur-containingfunctional group such as SH, although additional and/or alternativefunctional groups are possible without departing from the scope of thisdisclosure. For example, one or more functional groups such as Y and Zmay be a carboxyl group, a hydroxyl group, an ester, a carbonyl group,and/or a nitrogen-containing functional group.

FIG. 5 also shows various molecular interactions that may occur betweenthe surface-modified fabric and As(III) and As(V. Further, FIG. 5 showsvarious molecular interactions that may occur between thesurface-modified fabric and As(III) and As(V. It will be appreciatedthat bond formations other than those shown in FIG. 5 may occur withoutdeparting from the scope of this disclosure.

The following in regards to FIG. 5 is provided as an illustration of anoptional construction and not as a limitation. Specifically, asdiscussed, in some embodiments, an ion-barrier further may beconstructed on the surface of the fibers. Any suitable ion-barrier maybe constructed, for example, and not as a limitation, an ion barrier maybe prepared by attachment of a long chain hydrocarbon moiety onto thesurface of the fiber. For example, a hydrocarbon moiety may be used,including a lipid or fatty acid which may be attached onto the surfaceof the fiber. The attached lipid barrier, such as a lipid chain, ring,etc. may create a physical barrier to the internal surface of thefabric. Any suitable fatty-acid chain or the like may be used forattachment onto the fiber. The ion-selective barrier also could becreated by attachment or overlay of a semi-permeable membrane made ofhydrophobic materials.

The ion-selective barrier may include fatty acid chain extensions withcarbon chains of C4-C25. The carbon chains may extend away from the bodyof the fabric to form a physical barrier to cations, such as K+, Na+,Mg2+, and Ca2+. It should be noted that such cations may be of anincreased size due to hydration. Thus, although the fiber may be chargedsuch that various ions are attracted to the fiber, some large molecules(such as the highly hydrated cations) may be prohibited from enteringinto the fiber by the fatty acid chain extensions. Thus, the chains mayoperate as an ion-selective barrier, allowing small molecules to passthrough into the fiber, (thus trapping the less hydrated moleculeswithin the fiber), while physically preventing the larger molecules(such as the hydrated cations) from passing through to the trap.

The hydrophobic nature of the ion-selective barrier must be balancedwith the accessibility of arsenic to the selective functional groupsthat bind arsenic. Thus, the barrier must be sufficiently hydrophobic torepel the substantial cations (minerals), but be not so hydrophobic asto significantly decrease the rate of diffusion of As(V) which isnegatively charged as well as relatively hydrophilic organic toxins.Most of organic toxins are less hydrophilic or rather hydrophobic asshown by the log p values in Table 1. Therefore, those organic toxinswill be well adsorbed by ACFs and even some organic toxins with extendedcarbon chains (which are generally difficult to be removed) could betrapped by the ion-selective barrier.

For example, essential minerals, such as K+, Na+, Mg2+, and Ca2+ may besubstantially unable to penetrate the physical barrier presented by thecarbon chains. The essential cations may be considered to be repelledfrom the ion selective hydrophobic barrier. Thus, the essential cationsare retained in the treated water, thereby maintaining ionic homeostasisand mineral balance which are important for body health and boneremodeling as well as taste in the water.

However, toxins may be able to penetrate the barrier and thus may bereadily adsorbed by the fiber. The toxins become trapped within thebarrier. The chains may also be configured to allow arsenic or othertoxins to pass through and be trapped by the barrier. It should beappreciated that in some embodiments the carbon chains may be ofdifferent sizes along the length of the fiber or the fabric. In otherembodiments, the carbon chains may be of the same length along the fiberor fabric. The position of the chains may be dependent on theeffectiveness of the barrier. Moreover, in some embodiments, whereshorter length chains are utilized, the shorter length chains may bepositioned in relatively close proximity, while, in other embodiments,longer length chains may be more separated. Such spacing may beeffective as the longer chains may cover more area and provide anappropriate physical barrier without being as closely positioned asshorter length chains. Further, although shown as extended carbonchains, in some embodiments, the chains may include one or more rings,or other configurations, such that the carbon chains are considered acarbon barrier. It should be noted that the addition of theion-selective barrier to this water purification system will be optionaland depends upon the needs of people and quality of drinking water.

Although other suitable ion barriers may be prepared on the fiber, thefollowing method of constructing an ion barrier on the activated fiberis provided for illustrative purposes. Specifically, in one embodiment,a surface-modified activated fiber, such as an acid-treated activatedfiber, may be further modified to create an ion barrier by addition of afatty acid. The fatty acid may be as short as C4 or may extend to C25.In some embodiments, fatty acids with chain lengths of C14 to C17 may beused. It is noted that the carbon of the carboxyl group of the fattyacid is counted when discussing the number of carbons in the fattyacids. In other examples, the ion barrier may not be employed.

In an exemplary embodiment, an ion-barrier may be constructed on theactivated fiber by reacting a surface-treated activated fiber, such asan acid-treated activated fiber, with palmitoyl chloride in the presenceof an acid scavenger, such as pyridine, triethylamine,4-(dimethylamino)pyridine, Proton-Sponge®, and severalpolystyrene-divinylbenzene (PSDVB)-supported acid scavengers includingseveral PSDVB-supported piperidine compounds. The reaction may result inaddition of palmitoyl groups (C16) attached to the activated fiber. Itshould be appreciated that any other suitable carbon chain or carbonbarrier may be attached to the activated fiber, in addition to, and/oralternatively to, the palmitoyl groups.

Further the fibers may be modified to include both an ion barrier andimmobilized enzyme or microbial biofilm. The immobilized enzyme may beconfigured to decompose arsenic into smaller molecular ions. The ionsmay be trapped by the fabric. For example, positively-charged ions maybe attracted to a negatively-charged fabric. As another example,negatively-charged ions may be attracted to a positively-charged fabric.It will be appreciated that the fabric may be negatively-charged orpositively-charged. As another example, the fabric may includenegatively-charged zones and positively-charged zones for attractingpositively-charged ions and negatively-charged ions respectively.

Any suitable method may be used to immobilize the selected enzyme. Insome embodiments, it may be selected to covalently attach arsenatereductase, or other suitable enzyme, to the fiber. Any suitablebiochemical methods may be used to attach or otherwise immobilize theselect enzyme or enzymes. For example, coupling agents, and/or covalentlinkers, as well as other biochemical methods, may be used to immobilizearsenate reductase, or an alternative ion-selective compound, onto thefiber.

As described above, in one exemplary embodiment, the synthesizedselective adsorbent fabric may include one or more fibers with one ormore of the following: a hydrophobic layer adjacent to attached lipidchains, an ion-selective barrier formed by the lipid chains, immobilizedarsenic reductase capable of catalyzing the hydrolysis of arsenate toarsenite ions, for example, and other chemical reaction intermediaries,and hydrophilic pores capable of trapping other toxins and/or ions fromthe hydrolysis of arsenic.

Turning to FIG. 12, it shows repetitive application of toxic chemicalsolution on the column packed with 100 mg ACF-SBX. Loading capacity oforganic chemicals by ACF-SBX was determined as follow:

A solution (2.0 ml) containing 2 ppm each of atrazine, p-dichlorobenzene(p-DCB), diuron, 2,4-dichlorophenoxyacetic acid (2,4 D),N-nitrosodiethylamine (NDEA), bisphenol A (BPA), and diethyl phthalate(DEP) in pH 6.9 STW was applied each time. The applications wererepeated at least 300 times without any elution of above chemicalsexcept NDEA (after 200 times) which is known concerned toxic chemicalsdifficult to remove from drinking water. Since HPLC profile on theeluted through ACF-SBX was just flat. The eluted fraction (at 200 times)was subjected to more sensitive LC/MS after SPE extraction—concentrationof eluted solution. There were some background peaks (very minimal) wereobserved, but, no chemicals equivalent to the masses of applied sevenchemicals was found. Therefore, it is very likely that all the chemicalsrepeatedly applied were adsorbed and also no leaching out FIG. 12 showsthe experimental results.

From the above experimental results, the maximal operational capacity(95% to 100%) of 7 toxins was assessed by repeatedly applying thechemicals (about 2.0 ppm each). The resulting toxin concentration of 14ppm total toxins is about 100-200 times higher than the total toxicorganic chemical concentration at most sites of ground/drinking watercontamination (other than industrial waste water sites). The resultsindicate that if there is no strong competitive materials in ground/wellwater, an ACF-SBX module containing 100 grams of ACF will filter up to5-10 grams (5-10% of fiber weight) without leaching. Assuming a totalorganic contamination of 500 ppb (one of the highest cases in thedrinking water/well water), 14 liters of drinking water per day(standard for a four-member family), the filter would need to clear 7mg/day and 2.56 grams organic toxins/year. Therefore, unless extremeenvironments exist, such as very high concentrations of organic toxinsor natural organic matter (NOM), residents will not have to change thefilter for at least a year. Thus, the combination of ACF-SBX and ACF-SH(III) will create the powerful tool for water purification contaminatedwith both arsenic, toxic metals, and toxic organic chemicals.

Thus, the systems described above provide for a system capable ofremoving toxins from water for water purification. In an embodiment, thesystem comprises a purification chamber comprising a selective adsorbentactivated carbon fiber fabric including one or more selective functionalgroups that bind arsenic.

The fabric may be disposed to create a water flow channel in thepurification chamber. In one example, the fabric is in a spiralconfiguration. In another example, the fabric is in a flat layeredconfiguration. The system may further comprising a pump to move wateralong the flow channel. The one or more selective functional groups maybe included on a surface of the activated carbon fiber. The one or moreselective functional groups may include one or more of asulfur-containing group, a hydroxyl, a carboxylic acid, a carbonyl, anester, a nitrogen-containing group, and strongly-basic anion-exchangegroup. In an example, the selective adsorbent fabric includes a boundarsenic reductase enzyme.

The system may further comprise one or more functional groups to adsorbtoxic metals or toxic organic chemicals, where the toxic metals compriseone or more of lead, mercury, cadmium, chromium, nickel, iron copper,platinum, and palladium. The functional groups to adsorb toxic metals ortoxic organic chemicals may be included within or on a surface of theactivated carbon fiber.

The purification chamber may include an ion-selective barrier, forexample coupled to the activated carbon fibers. The system may beportable, or the system may be stationary, for example for use intreating a municipal water source. The system may include an inlet fromone of well or ground water.

In an embodiment, a water purification system comprises an inlet toadmit untreated water; a purification chamber comprising a selectiveadsorbent activated carbon fiber fabric having a surface including oneor more selective groups that bind arsenic; and an outlet to dischargetreated water.

The one or more selective groups that bind arsenic may comprise one ormore of a thiol selective group and a strongly basic anion exchangegroup. The fabric may be disposed in the purification chamber to createa water flow channel fluidically coupling the inlet to the outlet. In anexample, the fabric is disposed in a spiral configuration.

Turning now to FIG. 13, a method 200 for purifying water is illustrated.The water purification method illustrated in FIG. 13 may be carried outusing a water purification system as described in one of the examplesabove. At 202, method 200 includes directing untreated water to apurification chamber. The untreated water may be directed from asuitable source, such as ground water, well water, etc. The untreatedwater may include various toxins, including but not limited to arsenic.The untreated water may be temporarily housed in a reservoir, e.g., anuntreated reservoir, before being directed to the purification chamber.The reservoir may be separate from or integrated with the purificationchamber. Further, the untreated water may be directed to thepurification chamber via a pump, gravity flow, capillary action, orother mechanism.

The purification chamber may be a suitable chamber housing a selectiveadsorbent fabric adapted to trap arsenic and/or other toxins, such asthe purification chamber described above with respect to FIGS. 1A-1C andFIG. 2. The selective adsorbent fabric may include activated carbonfibers having selective functional groups on its surface which bindarsenic. The selective functional group or groups may includesulfur-containing groups, strongly basic anion exchange group, or otherarsenic-binding groups. Further, the fabric may alternatively oradditionally include bound arsenic reducatse, to enzymatically breakdown the arsenic, and/or an ion barrier. When the untreated water isdirected to the purification chamber, the untreated water passes overthe selective adsorbent activated carbon fiber fabric, where arsenicand/or other toxins are bound, trapped, or otherwise retained by thefabric. Further, in some embodiments, desired cations or other moleculesin the untreated water may not be trapped by the fabric and thus areretained in the water.

Thus, as indicated at 204, after the untreated water is directed to thepurification chamber, it is passed over the selective adsorbentactivated carbon fiber fabric in the chamber to create treated water.The treated water is then directed to an end location at 206. The endlocation may be a treated water reservoir separate from or integratedwith the purification chamber. In other examples, the end location maybe a facet, municipal water tank, storage or drinking vessel, or othersuitable location.

Thus, in an example, method 200 described above provides for a methodfor purifying water, comprising directing untreated water to apurification chamber; and passing the untreated water over a selectiveadsorbent activated carbon fiber fabric in the purification chamber tocreate treated water, the fabric including one or more selectivefunctional groups that bind arsenic.

Directing untreated water to the purification chamber may includedirecting well or ground water to the purification chamber via a pump.In an example, passing the untreated water over the selective adsorbentactivated carbon fiber fabric may include passing the untreated waterover a selective adsorbent activated carbon fiber fabric including asulfur-containing group. In an example, passing the untreated water overthe selective adsorbent activated carbon fiber fabric may includepassing the untreated water over a selective adsorbent activated carbonfiber fabric including a bound arsenic reductase enzyme.

It should be appreciated that although the purification chamber andassociated fabric is described for use in a water treatment system, thepurification chamber and associated fabric may be used in anypurification system. As such, the purification chamber and associatedfabric may be used in other systems that require removal of toxins froma fluid. For example, the purification chamber may be used to removetoxins from fish hatcheries, and other aquaculture based industries.

Further, it will be appreciated that the above toxin trap may be used totrap other types of toxins, including pathogens, viruses, bacteria, etc.In these systems, the traps may include an alternative adsorbent,specific to trap the select toxin. For example, such a system may beapplied to reduce or minimize the presence of toxins, includingpathogens, viruses, bacteria, etc. that may contaminate waterways andcontribute to waterborne diseases.

Although the present disclosure includes specific embodiments, specificembodiments are not to be considered in a limiting sense, becausenumerous variations are possible. The subject matter of the presentdisclosure includes all novel and nonobvious combinations andsub-combinations of the various elements, features, functions, and/orproperties disclosed herein. The following claims particularly point outcertain combinations and sub-combinations regarded as novel andnonobvious. These claims may refer to “an” element or “a first” elementor the equivalent thereof. Such claims should be understood to includeincorporation of one or more such elements, neither requiring, norexcluding two or more such elements. Other combinations andsub-combinations of features, functions, elements, and/or properties maybe claimed through amendment of the present claims or throughpresentation of new claims in this or a related application. Suchclaims, whether broader, narrower, equal, or different in scope to theoriginal claims, also are regarded as included within the subject matterof the present disclosure.

We claim:
 1. A method, comprising: treating a carbon fiber with heat inthe presence of air to form a heat-treated carbon fiber; treating theheat-treated carbon fiber with an oxidizer to form an oxidized carbonfiber; and treating the oxidized carbon fiber with a thiolating agent toform an activated carbon fiber comprising plural alkylthiol moieties andhaving a sulfur to carbon ratio for the activated carbon fiber of from0.3 to 0.4 by elemental analysis.
 2. The method of claim 1, wherein thealkylthiol moieties comprise CH₂SH.
 3. The method of claim 1, whereinthe alkylthiol moieties are CH₂SH.
 4. The method of claim 1, wherein theoxidizer comprises a mineral acid.
 5. The method of claim 1, wherein theoxidizer comprises nitric acid, sulfuric acid, peroxide or a combinationthereof.
 6. The method of claim 1, wherein the oxidizer comprises amixture of nitric acid and sulfuric acid.
 7. The method of claim 1,wherein treating the oxidized carbon fiber with the thiolating agentcomprises treating the oxidized carbon fiber with thiourea.
 8. Themethod of claim 1, further comprising isolating the oxidized carbonfiber prior to treating with the thiolating agent.
 9. The method ofclaim 8, wherein isolating comprises rinsing the oxidized carbon fiber.10. The method of claim 1, comprising: treating a carbon fiber with amixture of nitric acid and sulfuric acid to form an oxidized carbonfiber; washing the oxidized carbon fiber with water until the washingshave a neutral pH; and treating the oxidized carbon fiber with thioureaand hydrobromic acid to form an activated carbon fiber comprising plural—CH₂SH moieties sufficient to provide the sulfur to carbon ratio for theactivated carbon fiber of from 0.3 to 0.4 by elemental analysis.
 11. Anactivated carbon fiber fabric comprising the activated carbon fiberaccording to claim
 10. 12. A method for using the activated carbon fiberaccording to claim
 11. 13. An activated carbon fiber made by the methodof claim
 1. 14. The activated carbon fiber of claim 13, comprisinghaving an arsenic adsorption of at least about 0.02 mg/g from an aqueous200 ppb arsenic solution having a pH of from 2 to
 10. 15. The activatedcarbon fiber of claim 13, further functionalized with a moiety otherthan an alkylthiol moiety.
 16. The activated carbon fiber of claim 13,further comprising one or more of

a hydroxyl, a carboxylic acid, a carbonyl, an ester, anitrogen-containing group, or a strongly-basic anion-exchange group. 17.A system, comprising a purification chamber comprising an activatedcarbon fiber fabric according to claim
 11. 18. The method of claim 1,wherein the carbon fiber is heated at a high temperature of from 300° C.to 325° C.